The feasibility of continuous and economical microfabrication of timed-bioresorbable glass microspheres containing yttrium-90 (Y-90) at therapeutic concentrations has been successfully demonstrated using Y-89 surrogate in the Phase I research. The microspheres are uniform in size and chemistry, and the timed-bioresorption characteristics can be predetermined according to the isotope half-life and the dosimetry requirements. A dependable commercial supply of Y-90 glass microspheres will have a positive impact on localized radiation therapy worldwide. This Phase II research has the objective of making such a supply a commercial reality. The proposed microfabrication process can be streamlined and fully automated from Y-90 isotope extraction to packaged Y-90 microspheres ready for delivery and treatment injection. The microsphere production process will be optimized with regard to minimized personnel radiation exposure, maximized use of source radioisotopes, much shortened overall process time to preserve radioactivity, and above all, much reduced cost. Microspheres containing therapeutic concentrations of radioisotopes will be evaluated in vitro for radioactivity retention, biocompatibility, and completeness of bioresorption; and in vivo to demonstrate the efficacy of the Y-90 microspheres in treating tumor-bearing rodents. PROPOSED COMMERCIAL APPLICATIONS: Timed-bioresorbable glass microspheres containing Y-90 are ideal for direct intratumoral injection in the treatment of cancers such as the liver, pancreas, or the synovectomy of rheumatoid arthritis. Microspheres containing other radioactive isotopes such as P-32 can also be readily produced by the methods described.